1. Field of the Invention
The embodiments discussed herein are related to an integrated device having optical elements and electrical elements disposed on the same substrate, and a manufacturing method of the integrated device.
2. Description of the Related Art
Conventionally, a module is known in which an optical element such as a laser element and an electrical element such as an IC are disposed in a mixed manner on the same substrate (see, for example, Japanese Laid-Open Patent Publication No. 2007-72206). In the module described in Japanese Laid-Open Patent Publication No. 2007-72206, an optical element and an electrical element controlling the optical element are implemented on a substrate made of silicon (Si), for example. An optical waveguide may be formed on the substrate so as to be optically coupled to the optical element and to guide light to the outside.
In the module described in Japanese Laid-Open Patent Publication No. 2007-72206, the optical element and the electrical element are implemented on the substrate by flip-chip bonding. That is, the elements are implemented by forming bumps on the bottom surface of the optical element and the electrical element, contacting the bumps with the electrodes of the substrate, and applying heat and pressure for metal bonding.
Other than the module above, a technology is known in which an optical element such as a laser element is bonded to a substrate by surface-activated bonding (see, for example, Japanese Laid-Open Patent Publication No. 2005-311298). The surface-activated bonding, in short, is a method of low temperature bonding, employing the cohesion of atoms by activating the surface of a material by using, for example, plasma processing to remove an inactive layer such as an oxide film and contaminants covering the surface and bringing atoms having a high surface energy into contact with each other.
However, if functional elements made of different materials are disposed in a mixed manner on the described integrated device to obtain an advanced integrated device, precise optical coupling of the optical element disposed on the substrate and the optical waveguide formed on the substrate cannot be achieved due to poor alignment of the optical axes caused by cumulative deformation of the substrate with the optical waveguide due to the thermal history. In particular, as the number of optical elements and electrical elements disposed in a mixed manner increases, the number of processing steps increases, causing greater deformation of the substrate due to heat processing and thereby preventing a precise optical coupling of the optical element disposed on the substrate and the optical waveguide formed on the substrate. That is, an accuracy of submicrons in the positioning of the optical element and the optical waveguide, which is required for precise optical coupling, cannot be achieved.
If the optical element and the electrical element are implemented by flip-chip bonding as described in Japanese Laid-Open Patent Publication No. 2007-72206, since the optical element, the electrical element, and the substrate are thermally processed, positions of the components may deviate due to the difference in the coefficient of thermal expansion of each component.
If the optical element is bonded by surface-activated bonding as described in Japanese Laid-Open Patent Publication No. 2005-311298 after the electrical element has been implemented by flip-chip bonding, since the substrate is heated when the electrical element is implemented, the substrate becomes warped and the precision of the positioning of the optical element during the surface-activated bonding can be adversely affected.
Additionally, if the electrical element is implemented on the substrate by flow soldering, reflow soldering, etc., the same problem occurs since the electrical element and the substrate are heated. Thus, the precision in the positioning of the optical element and the electrical element disposed on the substrate of the conventional integrated device cannot be improved. Similarly, the conventional integrated device cannot achieve a precise optical coupling of the optical element disposed on the substrate and the optical waveguide formed on the substrate.